Train control



Jan. 29, 1929. v 1,700,703

R. c. LEAKE ET AL TRAIN CONTROL Filed Sept. 21. 1923 2 Sheets-Sheet IN VEN TORS Kama/ M Jan. 29; 1929. 1,700,703

R. c. LEAKE ET AL TRAIN CONTROL 2 Sheets-Sheet 2 Filed Sept. 21, 1923 BYMTT%NEY:

Patented .lan. 29, 1929.

RICHARD o. LEAKE AND onAaLns r. ES'IWICK, or Roonnsriin, m zo x,nss'reiiorls T0 GENERAL RAILWAY SIGHALCOMPANY, or :aocnnsrna'nuw YORK;

TRAIN CONTROL.

Application filed September 21, 1923. Serial No. 664,045.

This invention relates to automatic train control systems oi thecontinuous alternating current inductive type, and more particularly tomeans for tuning the various circuits of the car-carried apparatus sothat this apparatus will respond substantially to the same degree forvarious frequencies within a certain range.

Generally speaking, in the type of system to which the present inventionrelates alter nating current is transmitted through one or more suitabletraclrway circuits which inductively influence suitable amplifyingapparutus on the train for maintaining a relay energized in accordancewith the flow of such current. More specifically, one particular type oftrain control system of this general character includes a receiving;element located in front of the first axle of the tram which is ininductive relation with the rails of the tracltway and responds to theflow of current in one direction in one or" the rails, and in the otherdirect-ion in the other rail correspondto the usual track circuitcurrent and conveniently called the loop circuit current; and anotherreceiving element in inductive relation with the track rails andconstructed to respond to the flow oi current in the same direction inthe two rails in multiple, conveniently called the simplex circuitcurrent. On account 01" the limited current which may be applied inpractice to the usual tracliway circuit, and on account of thedifficulty of inductively detecting such a small track circuit currentthrouon an intervening; air gap, it is V I .whereby the currents in thewindings of the v relay are caused to be shifted in the opposite founddesirable to tune the windings of the inductive influence receiving;elements, to. a degree at least, in order to be able to .ints the r layener ed by the use of ordinary amplifying apparatus. in practice, the onin the track rails is derived from a trans scion line supplied "fromcorniuerciulapparatusg and the flCqllC. -y varies slightly.Consequently, it the rec 3 ele- ..ve the' r winding gs tuned 7 7 "ply toe at the frequency of the Slglltlllllff rd that ch-s 'ht variationschain of circuits and devices betvee'n the in accordance with track orloop circuit influence receiving element and one element of atwo-elementcarcarried relay, 1n which the winding ofthe receiving element is tunedto a frequency higher than the frequency of the-proposed signalingcurrent; and to provide a suitable series or-chain of circuits anddevices between the other orsimplex receiving element and theotherIe-lement-of the relay, in which the winding of the simplexreceivingelement is resonant to a frequency lower thanthe proposedsignaling i'requency, so that two overlapped resonance characteristicsare obtamed 1n the detectmg and amphfying apparatus for energizing thepolyphase relay,

The provision of apparatu'stuned in a man- I ner as thus far described1s, however, not 'entirely -satisfactory, because the two. trackwaycircuits mentioned preferably have currents flowing therein which aresubstantially in quadrature (displaced electrical degrees) so as to makethem distinctive, and

with two influence receiving elements tuned above and below thefrequency of the signaling currents, respectively, the reproducedcurrent for operating the relay will not be correspondingly displaced(in quadrature) unless'a compensatin shift in the phase of thesecurrents is made in a suitable manner. Therefore, as a further object ot-the present invention, it is proposed to provide means direction so asto bring them into quadrature,

or displace them substantially the same mun Figure 1. illustratesconventionally and in 1 a diagrammat c manner the devices ofthe mannerin which they cooperate;

2'graphically. illustrates the variation in phase relationfof thecurrents in the-re I car carr-ied andtrackway apparatus and the Yceiving elemcntsvas comparedwith,theinnected to suitable contact fingersand which is biased to assume a neutral position. contacts for such arelay R are shown conventionally in the drawings as comprising aplurality of fingers, cooperating with stationary contacts indicated byarrows, these fingers having a middle or neutral position and movable ineitherdirection to a normal and a reverse posit-ion, respectively. Thisrelay R also has two field coils or windings L'W and SW of suitableconstruction. If both of these windings are energized with alternatingcurrent displaced in phase, the rotor or vane of the relay is shifted inopposition to its bias in one direction or the other. If either ofthesewindings is deenergized, the movable element of the relay assumes itsbiased or neutral position. For reasons well recognized by thoseskilledin the art, the torque or operating force of the movable elementinsuch a relay depends upon the product of the currents in the two fieldwindings and also the phase displacement of these currents, the torquebeing a maximum for a given product of currents in the field windingswhen the phase displacement of these currents is 90 degrees.

This relay R has its field windings LW and SW connected to respond toloop circuit and simplex circuit currents, respectively. The loopcircuit field winding lfW of the relay R derives its current fromsuitable amplifying apparatus including thermionic amplifiers or audionsLA and LA and a trans former LT; and the simplex circuit field windingSW derives its current from a similar amplifying apparatus, includingthe audions SA and 8A and a transformer ST. Since the various circuitconnections between the influence receiving element LE and the fieldwinding law of the relay Rare substantially the same as that between theinfluence receiving element SE and the field winding SW the circuits forthe simplex circuit receiving element only will be traced; and the likeparts for the loop circuit receiving element LE will be given the samereference numbers with distinctive exponents L.

The filament circuit for the audio-ins Sil and A may be traced asfollows :--beginning' at the positive side of the filament battery 33,which in the particular system illustrated preferably comprises a 82volt oat tery, wires 34, 85, 36 and 37, filament of the audion 8A wire38, resistance unit 39, wire 40, filament of the audion SA wire ll,resistance unit 42, wires 48, i l, a5 and d6 back to the filamentbattery 33. it should be noted that this circuit includes resistances 39and 42. These resistances ar used to provide the necessary negative biasoi the grids of the audions SA? and Sr? with respect to their respectivefilaments, so that these gric s do not draw current. In the particularsystem disclosed good results have been obtained The by choosingresistances which cause't' e voltage of the grid of audion SA tobe n'etive to the midpoint of its filament b volts; whereas the grid of theaudion S negative with respect to the said poin filament to the extentof 27 volts. I

The grid circuit for the audion gA may be traced as follows :beginningat the'windine' l8 of the simplex element SE, wi stare sistance unit 50,wires 51 and 52, grid ofthc audion 6A to the-filament of this aud'ion,througl i the wire 41, resistance unit 42, wires 4-3, 53, 54 and 55backto the winding 48- of the simplex element SE. The winding 48 inseries with resistance unit 50 is shunted by a condenser 56 for purposesmore clearlydescribed hereinafter. q

The plate circuit forthe audion Sil may be traced as follows:begi-nningat the plate battery 60, wires 6l, 62,63 and 64, primarywinding of the transformer ST, wire 65, plate of the audion 5A to thefilament of this au'dion, to the filament battery 33', wires- 3-1 and 66back to the plate battery 60.

The grid circuit for the audion 8A may be traced as follows :'beginningat the secondary winding of the transformer ST, wires 67 and 68, grid ofthe auction SA to the filament of this audion, through the filamentcircuit and wires 69 and 70 back to the secondary winding ofthetransformer ST. The

secondary winding of this transformer'Sl is shunted by a condenser 71,for the reason more clearly described hereinafter;

, The plate circuit for the audion Si-i may be traced as follows:beginning at the plate battery 60', wires :61, 62,- 63 and 77,inductance or choke 78, wires 79 and 80, plateof the audion 8A to thefilament of this audion, through the wires 37, 36, 35 and 66 baclr tothe plate battery-60. p j

lheinductance 7,8 is shunted by' a partial circuit including the windingSW of there lay The circuit for this winding SW which permits the flowof alternating current, due to changes of uni-directional current fiowint'he inductance 78, may be tracedas follows :beginning at the positiveside of the plate battery 60, wires 61, 62, 63and W, inductance 78,wires 7, 9 and 81, blocking" condenser 82, wire 83, winding SV/ of there-- i, la v battery 60. r

. ln order to llliI OTi'lTtllQ enginer of tra'liic conditions ahead,suitable signals are preferably provided at a convenient point in thelocomotive cab or anyother suitable place,

wires 84, 3'5 and 66 back to the plate. I I

vhichrespond to the different. indicating" as shown, the caution lamp Yis energized when the relay is energized in the reverse direction, andthe red lamp Rd is energized if the relay is deenergized.

Suitable apparatus is preferably provided on the railway vehicle tocontrol the train in any suitable manner. his apparatus preferablyincludes a speed-responsive device and an elcctro-pneumatic brakecontrol device, and suitable means for actuating the brake controldevice and applyin the brakes of the vehicle if the speed of the trainis excessive. In order to simplify the description of the presentinvention, a caution device Ca has been illus fated to properly controlthe train in a' caution block. control device is of the normallydeenerg'ized type, and is n'iaintained energized under clear traliicconditions by energy flowing from one terminal B of a suitable source ofsupply to the other terminal C of said source as readily traced in thedrawings. This device Ca is only energized when the relay it is in itsnormal energized condition.

Another control device adapted to control the train in anyniannerdesired when movin throu h a dan er block has been L: C t) illustratedby the device Dr, as shown. This device is energized when the relay R isenergized in either its normal or its reversedirectiorn This devicepreferably limits the speed of the train eventually to a predeterminedlow value of, say miles per hour, and then maintains the speed solimited as long'as this device Dr is deenergized.

Operation-Let us assume that "he block J is occupied by another train,or is in a dangerous condition for some other reason,

and the track relay 5 is deenergized. With the track relay 5 at theentrance to the block J deenergized, the three sections from thebeginning to the ex; end of the block I are provided with normal simplexcurrent, reverse simplex current, and zero simplex current,respectively.

With the simplex circuit current flowing in the normal direction, thatis, in a predetermined phase relation to the track circuit or loopcircuit current, both field windings of the relay R are energized bycurrents di placed in phase sub. tantially the sameas the phasedisplacement of the loop and simplex circuit currents, and consequentlythe movable element of the. relay assumes its normal position shown,lighting the green lamp G and energizing: both the caution controldevice Ca and the danger control device Dr. In other words, with therelay R in its normal position, a clear or proceed cab signal isdisplayed and the speed restrictions or other control enforced by thedanger and caution control devices are not in eii'ect. The speed of thetrain under such clear trahic conditions may be unlimited, or ifdesired, this normal running speed may be limited to some arbi- Thiscaution train 7 if) M. ll.) comes to a weaves t-rary maximum, such asmiles per hour. The relay R is maintained in the normalconditicn, withthe results just noted, while the train is travelingthrough the block Hunder the clear tratlic conditions assumed to exist.

As the train moves into the block I, the block J next in advance beingassumed to be occupied, there is no change in the position of the relay3 during the travel of the train over the first section of this block 1.between the balancing resistances 7 and 8, for the reason that thesimplex circuit current is still of the normal relative polarity orphase relation. This p rticular arrangement has been selected toillustrate how the caution control may be made effective at someselected point beyond the caution signal itself,.or the actual entranceto the caution block, this condition existing more particularly in thecase of long blocks that are longer than the braking distance necessary;but it should be;

understood that the balancing resistances 7 and 8, together withtransformer 9, may be omitted, and the balancing resistance l5 locatedat the joints 2 marking the entrance to the caution block.

[is the train moves beyond the balancing resistance 15, the relationbetween the loop and simplex circuit currentdetected by the car-carriedapparatus is reversed; and the relay llchangcs to shift its contactfingers to the reverse position, thereby deenergizing' the caution traincontrol device Ca but maintaining the danger control device Drenergized. Also, the green lamp G is extinguished and the yellow lamp Yis lighted. lhe engineer will. therefore, be required to reduce orgovern the speed of the train in accordance with the permissive speedset up by the caution speed device Ca. In one arrangement, the action ofthe caution speed device compels reduction in speed to intern'iediatespeed of, say, 40 miles per hour.

As the train passes the point D, it is entirel; leprived of simplexcircuit current and the ielay is deenerg'izcd, its field winding Filhaving no current therein. 7 The engineer is now required to govern hisspeed in accordance with the requirements of "he danger train controldevice or there is an autom tic applicationof the brakes. The dangercemrol device is made effective at the point D and before the ii, i. ofthe blocl; l: is read in Ol'tlQllO assure that the train reachesprodeterinined safe low speed (say stop before reachthe end of theblock.

[is he train proceeds intothe block J, this lo i tillbeinp; occupied bysaid another ain, the relay ismaintained deenergized re rdle s ofsimplex current flowing in the simple circuit of the block J. Thisistrue because no loop circuit current, or at least not an appreciab'leamount, will be flowing, so that the relay it is deenergized primarilyon account of the lack of current flowin in the Winding IIW of the relayR. Consequently, the restriction in the movement of the train isContinued so that it can not exceed said minim 'im speed limit until thesaid an other train leaves the block J. i As soon as this occurs thetrain in question is no longer restricted to this low limiting speedunless the train has passed the point D of the block J. Net, since thepresent system is based on the principle of continuous control, or apermanent communicating link between the train and track relays ahead,the train Will be immediately released andpermitted to proceed as soonas tralfic conditions ahead become more favorable, all in the mannerWell known by those familiar with this type of continuous inductivetrain control system. 1

'Co nstrmts of elements of the mucous carcarried decides-in order toobtain the desired performance of the car-carried apparatus undervarying frequencies, a varying amount of current fiowin in the simplexand loop circuits, respectively, reasonable variation in the phasedisplacement between these lTWO currents and other varying conditionsencountered in practice, the various circuit portions of the car-carriedcircuits are tuned and adjusted in a predetermined manner to bepresently described. The variation in the frequency of the alternatingsignaling current to be picked up and amplified exists and must becompensated for, because this current will in practice be derived from atransmission line supplied With current from commercial apparatus andWillhave the small frequency variations ordinarily found in commercialpower sources. The amount of current in the loop or track circuit variesin accordance With the location of the train in the block, being amaximum with the train at.

the exit or feed end of the block and a minimum at the entrance end'otthe block. Variation in the phase relation of the currents in tiretracku'ay loop and simplex circuits is occasioned by thedifferentelectrical characteristics of the blocks, due tochanges inballast resistance, location of the train in the block, and otheri'actoi's.

previously stated, it is desirable to time more or less sharply thecoils ofthe receiving elements so as to obtain the maximum voltage forapplication to the grids of the vacuum tube amplifiers for the minimumamount of signaling current in the track rails. Roughspealring, it hasbeen found that, by the arrangement shown I and hereinafter eX- plained,the tuning of the coils of the receiving elements serves to give aninput voltage for the vacuum tube amplifiers which is from to 10 timesthe voltage induced in these coils. Such voltage increase ormanifestation is characteristic of voltage resonance and very desirablein train control systems of this type. Hence, a condenser, such as 56,is-connected in cries Withthe coil, as 48, of each receiving element.

lVith such an arrangemenu it is evident that there is a particularfrequency ilorw'hich the combination is resonated and the voltageequallyevident that for other frequencies the voltage Wlll be lower.Similarly, for the particular frequency for which the receiving coil istuned, the induced voltage and current in this coil are in phase Witheach other and have a definite phase relation to the current in thetrack rails producing such voltage and current; Whereas for a differentfrequency, the current in the coil of the receiving element and thevoltage across the condenser which is the potential applied to theamplivtier) does not have the same definite phase relation to theinducing current in the trac'l Way circuit, due to the fact that forsuch different'trequency there is more inductive reacross the condenseris a maximum; and it is actance in the tuned circuit than condensivereactance, or vice versa. the receiving coils are tuned sharply toresonate at a predetermined frequency, such as 60' v practice. it may besaid that the present invcntion deals principal-lyivith the problem ofarranging or ad usting the circu ts and devices on the locomotive orother vehicle, so as to attain substantially uniform torque tor therelay under the varying conditions of frequency encountered in practice.

For the purpose oi explaining the nature and iuulerlying principleOf'illllS'lllVGHlTlOll, it is assumed that the normal signalingfrequency is 60 cycles, and that compensation should he; made forvariation of '2 cycles either way. In other words, in this explanation,it is assumed that the equipment is designed to give a substantiallyuniform torque for the relay R for a range of frequencies be tween '58and 62 cycles per second,'it being understood of course that this ismerely illustrative. v f

As a further aid in explaining this inven tion, certain curves or graphshave "been shown Figs. 2 and these being drawn on the basis of certainassumed conditions which are of course susceptible of considerablevariation in practice. Fig. 2 illustrates the phase relation of thecurrent in the coils of the loop and simplex circuit elements withrespectto the voltage'induced in these respective coils -lor differentfrequencies. Thehorizonta-l distances or abscissa represent fre- 1Consequently, if

quencies, and the vertical distances or ordinates denote phase an le,positive phase angles or leading current being on the upper half of thefigure above the horizontal line, and a negative phase angle or laggingcurrent below said line. 1

Fig. 8 illustrates in two separate groups of curves to differentordinates, the variation in the current in the coils and also in thetuning condenser of the loop and simplex circuit elements, as thefrequency varies, and also the voltage across the tuning condenser forsaid elements.

As previously stated, the torque of the relay R depends upon the productof the currents in its respective field windings. [assumingproportionate amplification throughout. the working range of voltages,the currents in the field windings of the relay are proportional to thevoltages impressed upon the input circuits of their respective ampltiers. In other words as the voltage across the condenser 56 for thesimplex circuit re ceiving element SE increases or decreases, it may beassumed that the current in the field windings SW of the relay It correspondingly increases or decreases. It has been pointed out, however,that this voltage changes with the frequency, and hence the current insaid field winding likewise varies. Thus, if both of the receivingelements are tuned by their respective condensers to resonance for thesame frequency, an increase r decrease in this frequency would result indiminution of the current in both field windings of the relay andresult. in a lower torque. It is this condition that the particulararrangement of this invention, among other things, is proposed toremedy.

Generally stated, according to this invention, the condenser 56 inseries with the coil 48 of the simplex circuit receiving element SE fortuning thiscoil, is preferably chosen,

or adjusted, to a capacity approximately 20% more than that. required toproduce resonance for the normal frequency of (it) cycles; andsimilarly, the condenser 56 is adjusted with about 20% less capacitythan required to produce resonance for said normal frequency. In otherwords, the coils of the two receiving elements are tuned, not to thesame frequency, but to different frequencies. More specifically, on thebasis of the assumptions hereinbefore mentioned, for arange'offrequencies from 58 to 62 cycles, one satisfactory arrangementis to tune the coil of the simplex element SE for resonance at about 54cycles and the coil of the loop circuit element LE for resonance atabout 65% cycles. This particular arrangement hasbeen indicated in theillustrative curves, as apparent from Fig. 2, the points of resonan'cebeing shown for the frequency producing zero phase displacement.

Assuming now that the coils'of the two receiving elements are tuned offresonance for the normal signaling frequency, as just stated, andreferring to Fig. 2, it will be seen that the induced current andlikewise the voltage across the tuning condenser is not the maximum forthe normal frequency of 60 cycles but is an intermediate value.Referring particularly to the voltagecurves in Fig. 3, it will be notedthat these curves have substantially'the same general form and slope,especially over the range of frequencies for which the equipment isdesigned, namely, between 58 and 62 cycles. It will also be. noted that,as the normal frequency of 60 cycles is increased, for example, to 62cycles, the voltage across the condenser 56 for the simplex element SEdecreases, while the voltage across the condenser 56 for the loopcircuit receiving element LE increases; and on account of the similarityin this va riation, the product of the voltage remains practicallyconstant throughout the band of frequencies in question. For example, at58 cycles the voltages are 2.2 and 2.4 with a product of 5.2; at afrequency of 60 cycles, the voltages are 1.7 and 2.9 with a product of41-.93; and at 62 cycles, the voltages are 1.3 and 3.7 with a product of4.81. In short, the products of the voltages or potentials in pressed onthe amplifiers remain substantially constant, one increasing as theother decreases with a change in frequency, and vice versa, so that thecurrents in the field windings of the relay R change, one increasing andthe other decreasing, with a change-of frequencies, their productsremaining substantially constant and the torque nearly uniform.

The arrangementjust described for maintaining uniform relay torque fordifferent frequencies, consisting of tuning the receiving elements tohigher and lower frequencies respectively than the normal frequency,

serves admirably for this particular purpose.

but introduces additional factors and consideratirms. Mention has beenmade of the fact that the phase relation of the induced currents in thecoils of the receiving elements varies with respect to the inducedvoltage as the frequency varies. If such variation in phase relationwere truthfully reproduced proportionally throughout the amplifiers andup to the field windings of the relay R, the net effect upon the relaywould be substantially the same, the currents in its field Windings bothbecoming more leading or lagging, as the case may be, and to thesamedegree. Exact similarity and faithful reproduction of phase relationthroughout an amplifier arrangement, particularly with apparatus builtin quantity on a commercial basis, is not easy to obtain or maintain,with the result that compensating adjustments are desirable and almostessential.

Another desirable attribute of the car equipment for a system of thecharacter un-- der consideration is that there should be no ultimatechange in phase relation produced by the car apparatus by itself, thatis, the phase relation of the currents in the windings of the relay Bshould be the same as the phase relation between the currents in thesimplex and loop circuits. This is desirable for several reasons, andmore particularly to avoid the possibility of false operation underpeculiar conditions. To illustrate, suppose that the balancingresistance 16, for example, should have its connection to one of thetrack rails broken. This Would cause all of the simplex circuit currentto flow in the other rail and pass under'one of the loop circuitreceive-rs'LE. Such current Would induce a corresponding voltage in thecoils of the receivers LE and apply it to the grid ofthe vacuum tube LA,the current being confined to one rail so that there could benobalancing effect due to the Way in Which these coils are Wound. If theexistance of such abnormal simplex current and its action upon theamplifier for the loop circuit produces upon the Winding Ll/V of therelay R the same effect as the regular or authorized loop circuit, thenfalse operation of the relay might occur, that is,the relay might beenergized directly behind a train in the same block Which would shuntout the loop circuit current but Would not change the flovv of the falsesimplex current all in one rail. As aremedy for this possibility, it isproposed to arrange the loop and simplex circuit receiving elements andtheir amplifiers so as to have inherently no phase displacementandproduce all of the phase displacement, necessary for operation of therelay R, in the trackway circuits. With such an arrangement, falseapplication of the simplex circuit to the loop circuit receivingelements could not produce any improper effect upon the relay, sincethis current would he in phase with the regular simplex circuit currentin the other Winding of the relay, and this relay, as already explained,requires a phase displacement in the currents in its iield windings in;order to operate.

Generalizing, it is desirable, for the reasons indicated, and others notrequiring specific discussion, to provide an organization of circuitsfor receiving loop circuit current, and also for receiving simplexcircuit current,

which produces no phase shift on the can.

in order, however, to maintain substantially uniform torque on therelay, the coils for the simplex and loop circuit elements have already,as previously explained, been tuned oft resonance for the signalingfrequencies, so

to speak, with the result that at the signaling I frequency one islagging andthe other is leading With respect to the currents in thetrack rails producing such currents.

This condition just discussed is bestexplained by referring to Fig. 2,from which it natin current in the coil of the loop circuit iecondenser, leads its induced voltage by about 4:8 degrees at the normalfrequency of on account of the. smaller value of i 60 cycles, Whereasthe current in the 'coil of i the 316K receiving element lags behind itsind cing voltage by'about 59degrees. In order to bring the currentsapplied to the windings of the relay R back into phase, it is necessaryto make a similar compensation in another part of the operative chain between the receiving coil and the relay Windings, more specifically inthe amplifier. This is accomplished by using an inductive or rear sivecoupling between the first and second I 1 stages of the amplifier,namely, a transformer 81 or LT, and tuning these in an opposite fashionby a condenser 71 or 71%. I

To illustrate, assuming the'condenser 56 adjusted to resonate the coilsof the loop cir-' cuit receivers for a frequency higher than the normalfrequency and the condenser 56 adjusted to tune the coil of the simplex.receiver for a frequency lower. han the normal frequency, then thecondensers 71 and 71 can be selected or adjusted in either of two Waysto produce the desired compensation. Ac-

cording to the first method, the condenser 71 is selected to make thecurrent derived from the first amplifier LA of the loop circuit devicestill more leading, and the condenser 71 Elli to give a still morelagging current, so as to bring about a phase difference of 180 degrees.

According to the other method, Which is con- 7 sidered to be preferable,the'condensers '71 and 71 are selected or adjustedto bring the currentsback into phase, that is, With the current in the loop'circuit chain ofdevices leading as shown in Fig. 2, the condenser 71 1's justed to givea compensating lag. It is, of

course, evident that if the condenser 56 gives a lead of L8 degrees, thecondenser not necessarily give a lag of the same angle, so long as'thecondensers 71 and 71 together compensate for the total phase angledifienence. In other Words, assuming the condenser 56 gives a lead of4.8 degrees, as shown in Fig. 2, the condenser 71 may beadjusted to givea lag of,say, 58 degrees, instead of 48 degrees, or a 10 degreeover-compensation, but'in that case thecondenser 71 Would be adjusted togive a lead of 10 degrees less, or

.1.8 degrees, instead of 58 degrees, accordingto i the values assumedandshovvn in Fig. 2.

The transformers ST and LT have been referred to as used for. thepurpose of obtain,- ing a compensation in the amplifiers to bring aboutzero degree phase displacement; but it should be understood thatthesetransformers have other advantageous characteristics. For example, thesetransformers introduce an additional tuned element in the operativechain of devicesbetween the currents in the 71v need trackway circuitsand the windings of the car relay; and consequently these transformersgive greater selectivity and render the whole system less susceptible tooperation by currents of frequencies widely different from the normalsignaling frequency. It may be said that this feature ofselectivity isdesirable more particularly in the case of railroads emwith the sameeffect as described in connection with the coils of. the receivingelements. Qhe curves or graphs in the case of the trans formers, beingsimilar to those shown in Figs. 2 and 8, have not been illustrated; andin view of the foregoing explanation it .is thought to be unnecessary todiscuss this scheme of selection or adjustment of the constants forthese transformers.

The desired phase displacement of the currents in the simplex and loopcircuits on the trackway may be obtained in accordance with any one ofthe well-known expedients employed in connection with alternatingcurrent track circuits. According to the arrangement illustrated, whichis preferable for ordinary conditions, the simplex circuit is maderesistive, so that the current therein is substantially in phase withthe transmission line voltage; whereas the loop circuit is madereactive, so that the current therein lags behind the transmission linevoltage. Forthis reason, the reactance l is introduced in series withthe secondary of the transformer 3, this reactance serving the purposeof the usual limiting reactance or resistance employed to limit'the flowof current as a train approaches and stands directly over the feed endof the track circuit.

It may be explained here that the invention hasbeen shown in connectionwit-h alternating current track circuits,.but the same principles areapplicable to direct current track circuits, the alternating currentused for train control purposes eing superimposed upon the directcurrent, as for example, by connecting the transformer feed in serieswith the track batter As previously stated, it is considered to bedesirable in systems of this character to have no phase shifting by thecar apparatus, and have the phase displacement of the currents in thefield windings of the relay correspond with the phase displacement ofthe currents flowing in the simplex circuits on the track way. Based onthis pren'iise, the car apparatus may be readil adjustedto function inthe desired manner in the following fashion First, the coils of thereceiving elements are tuned off resonance to frequencies higher andlower than the norn'ial frequency. Then with these receiving elementsenergized by currents exactly in phase, the condensers Ti and 71 areadjusted so thatthere is no torque produced by the relay, Theseadjustments, it may be added, are preferably made after trial withvariations in frequency and strength of current in the tracl-zwaycircuits, such as would be encountered, in practice. After obtaining anadjustment of the car apparatus in this manner, the currents in thetrackway and loop circuits are thrown out oi' phase through anglescorresponding to that likely to be encountered in practice, thesecurrents respectively reversed and cut oil, and the to que of the relayR noted.

Mention has been made of the fact that there is considerable variationin the amount of loop circuit current influencing the receiving elementsLE as the train travels through block. So long as the car equipment issulliciently sensitive toproduce reliable operation of the car relaywith the minimum amount of loop circuit current, existing when the trainfirst enters a block, the additional energization of the relay .by theincrease of loop circuit current is not particularly objectionable; butit may be explained that this condition is under control and may be dulycompensated for by reason of the saturation or overload characteristicsof the vacuum tube amplifier. In other words, the amplifiers for theloop circuit particularly may be worked at such a point that excessiveloop circuit current does not produce excessive relay current.

The condensers 82 and SQ in series with the iield wind ings of the relay1%, are provided primarily to prevent the direct current from the platebattery 60 flowing through these windings, and these condensers areessentially blocking condensers. These blocking con densers 82 and 82 ofcourse reduce the inipedance of the circuits including the hold windinof the relay by compensating for the reactive component; and in practicethese conden ers are preferably of the value to produce resonance forthe normal frequency, that is, the condensive reactance of thesecondensers made equal to the inductive reacta'nce of the field windingsof the relay. The tuning of the field windings of the relay, however,does not produce very sharp resonance because there is included in thetuning circuit the high internal resistance of the vacuum tubeamplifier. In other words, the field windings of the relay do not have asharp or peaked resonant curve and respond much the same over the rangeof frequencies applied thereto.

This well known fact thatresistancein the tuning circuit flattens orbroadens the resonance curve may also be utilized in connection with'thereceiving elements and it is found desirable in many instances toinclude in series with these elements a resistance unit 50 which may beselected or adjusted to give a more flexible control'ov'er the constantsof these two circuits and promote stability of thesystemf Summarizingthe features of this inven tion, it will be observed'that the system oftrain control of the continuous inductive type employs two separatetrackway circuits, being conveniently termed the loop and simplexcircuits. The currents inthese circuits are derived from a transmissionline of 'cornmerout departing-from the nvention.

cial characteristics with the usual frequency variations, and thesecurrents are displaced in phase" by any one of the well known expedientsand are'individually controlled in the specific manner described to givethree distinctive controlling conditions, namely, simplex circuitcurrent normal, simplex circuit current reversed, and simplex circuit orloop circuitfcurrent cut off. Uniform torque for the car'relay ismaintained by adjusting thereceiving elements to frequencies higher andlower than the normal frequency; or, in other I words, these receivingelements are tuned ofi resonance. These tuningconditions are selected togive a substantiallyuniforin product of the voltages impressednpon'theamplifiers throughout the range; of frequency variation toheencountered'. v

In order to have 'thedesired' feature of zero degreephase displacementby the car-apparatus an additional reactive device (couplingtransformers) is introducedin each operative chain between the receiving-elements and relay, and-this ad'ditional'device is tuned 0E resonanceto give a constant procluct of voltage and uniform relay torque and alsoso as to compensate for the phase change produced by the tuning of thereceiving ele ments. In a sense, it may be said that each of" the chainof devices for the loop and simplex circuits has one link thereoflthereceiving coil) tuned to resonance for a frequency con siderablydifferent than the normal signaling frequency, and another link(coupling transformer) tuned fora frequency also considerablybutoppositely different from the signaling frequency. These tunings aresuch that the ultimate result is proper operation of the relay inproducing substantially uniform torque for a. range of frequencies, sayfrom 58 to 62 cycles, without'sacrificing the efficiency 'andadvantagesof tuned circuits and without departing from the safety principle ofhaving car apparatus operable only by trackway currents which are.displaced in phase. I

The present inventlon provides, a for trai'ismittlng induct vely any onetherefore,

fof threedistinctive] control influences to a vehicle at any andall-poin-tsxin. its-travel,v with due allowance and compensation to meetthe conditions: actually encountered in prac-- tice, more particularlyvariations-in frequency, and without sacrificing ith'eiadvantages' oftuned circuits. t should be understood that.

the specific organization of devices and cir cuitsherein shown anddescribedismerely illustrative of 1 the invention, and that the,invention is not limited to this specificiembodiment.Forexample,whileapolyphase relay What-we'claimis V. v

1. In ail-automatic train control system, the combination ortrackwaymeans for transmitting currents in two distinct trackway circuits, oneof. which consists of the usual 'trackcircuit; and car-carried apparatusincluding influence receiving elements having windings locatedin'inductive relation with said trackway circuits, condensers connectedin multiple with sa'idvwindings having capacities to tune these windingsto higherand lower frequenciesrespectivelytha n the "pro- 'posedsignaling -;frequency,- af two element electro-respons'ivedeviceoperated in res onse to currents flow ng in the-windings o saidelements, andtr'ain control means governed by said electroresponsivedevice.

2. In air automatic train-- control system,

the combination of trackwa-y means for transm tt ng currents in twodistinct rtrackw ay circuits, one of which consists of the-usual trackcircuit; and car-carriedapparatus including influence receiving elementshaving windings located ininduct-ive relation with said trackwaycircults, condense-rscon-nected in:-,multip'le with said Windingshavingcapacities-to time these windings to higher and lower frequenciesrespectively than I the proposed signaling frequency, two am lifyingQdevices having-their input circuits connected to the terminals of saidcondensers, atwo element,

relay having its windings connected'tothe output circu-its ofsaidamplifying devices, v andtrain control apparatus governed-by said relay;

3.- In an automatic train control system,

the combination of trackway means for transmitting currents in'twodistincttrackway circuits, one 'o-fwhichconsists of the usual trackcircuit; and'car-carried apparatus including infiuence receivingelementshavlng windings locatedininductive relation with said trackway circu ts,condensers connected in multiple with said windingsrh-aving cai pacitiesto tune these windings to higherv and the prolower frequenciesrespectively than posed signaling frequencygtwo' amplifying devicesconnected to respond to the potentialsacross said condensers havinginductive output Circuits, a polyphase relay having its wmdmgsconnectedto said output circuits,

and means for tuning said output circuits so as to cause the phasedisplacement between I the currents flowing in the two windings of therelay to be substantially the same as the phase displacement of thecurrents flowing in-the trackway circuits.

4. In an automatic train control system,

the combination of trackway means for transmitting currents in twodistinct trackway substantially the same amount as are the cur-.

rents flowing in said trackway circuits.

5. Car-carried apparatus for automatic train control systems of the typein which two distinctive trackway currents are transmitted along thetrackway, one of which flows in the usual track circuitahead of thetrain comprising, a two-element alternating current relay each elementhaving a winding,

two inductive influence receiving elements located in inductlve relationwith said trackway circuits, two chains of circuits and devicesconnecting said-receiving elements and the windings of said relay,certain of the elements of said chains being resonated to frequenciesdifferent from the frequency of the proposedtrackway currents. 6.Car-carried apparatus for automatic train control systems of the type inwhich two distinctive trackway currents are transmitted along thetrackway, one of which flows in the usual track circuit ahead of thetrain comprising, a two-element alternating current relay each elementhaving a winding, two inductive influence receiving elements located ininductive relation with said trackway circuits,tw0 chains of circuitsand devices connecting said receiving elements and the windings of saidrelay, certain elements of eachrchain being resonated 'to different frequencies both above and below the proposed frequency of saidtrackwaycurrents, and the corresponding elements of the two chains beingresonated to frequencies above and below, respectively, the proposedfrequency of said trackway currents.

. '7. Car-carried apparatus for automatic train control systems of thetype in which two distinctive trackway currents are transmitted alongthetrackway, one of which ourrents flows in the usual track circuit aheadof the train comprising; a two-element alternating currentrelay eachelement having a winding; two inductive influence'receiving elementslocated in inductive relation with said trackway circuits; two chains ofcircuits and devices connecting said receiving ele ments to the windingsof said relay; each of said chains including, two audions having theirfilaments connected in series, and a resistance unit in the circuit ofsaid filaments contained between said filaments'a'nd having an ohmicresistance of a value so that the filament current flowing therethroughwill produce the proper grid bias in one of said a-udions with respectto the gridbias of the other audion. f q p 8. In an automatic traincontrol system, the combination with separate trackway cir-. cuitsincluding track rails and energized subjectto control in accordance withtraffic cOnditions by alternating currentsof-thesame frequency butdifferent in phase, a two-element alternating current relay on avehicle,

and means on the vehicle inductively influenced by the alternatingcurrents in said trackway circuits for amplifying the energymanifestations produced by such currents and applying the energy soamplified to said relay without phase distortion and giving asubstantially uniform torque for" the relay for all frequenciesthroughout a predetermined range. 1

'9. In a continuous inductive impulse communicating means fortraincontrol purposes,

the combination with a two-element alternating current relay on avehicle, of receiving coils and amplifiers supplying current to thefield windings of said relay, and means tuning said receiving coils andamplifiers to pro- .vide a substantially constant product of thecurrents in the field windings'of said relay for all frequenciesthroughout a predetermined range.

10. In a train control system of the char-ace ter described includingtrack rails normally having alternating signaling current flowingtherein, separate receiving elements having coils and condensers tuningsaid coils, one to a lower and the other to a higher frequency; than thenormal signaling frequency. 7

11. In a train control system, the combina- 'tion with trackway circuitsenergized with alternating current differing in frequency from a normalthroughout a range of fre-. quencies, of a car-carriedtwo-elementalternating current relay, and amplifying means detecting theflow of alternating current in said trackway circuits and supplyingcurrent to the field windings of said relay, said currents in said fieldwindings having the characterized by the provision of means forproducing a substantially constant torque in the moving element of saidrelay throughout a predetermined range of frequencies.

13. In an automatic train control system of the character described, inWhich the 0peration of a two-element alternating current relay on avehicle is controlled by the presence and absence and also relativephase relation of alternating currents in two trackway cir-v cuits, theprovisionof means for maintaining a substantially uniform torque forsaid relay throughout a predetermined range of frequency variation.

' 14. Car-carried apparatus for automatic train control systems of thetype in which two distinctive trackway currents are transmitted alongthe trackway, one of which flows in the usual track circuit ahead of thetraincomprising; a two-elementalternating current relay each elementhavlng a w1nd1ng; tw'o 1n-. ductlve influence receiving elements locatedin inductive relation with said trackway circuits; two chains ofcircuits and devices con necting said receiving elements to the windingsof said relay; each of said chains includin an audion having its platecircuit divided into two branches in multiple one of which includes aninductive reactance and the other of which includes a winding of saidrelay and a condenser in series, whereby the di-. rect currentcomponent'of the plate circuit current does not flow through the windingof said relay.

In testimony s gnatures.

. RICHARD o. Luann; CHARLES F. "ESTWICK.

whereof we hereby .affix our

